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The loss of nitrogen (N) can be very high in rice ( Oryza sativa L.) fields, particularly in the irrigated rice cropping systems with very poor water control. Previous studies have reported very low (30 %) fertilizer N use efficiency by broadcasting in irrigated cropping systems. The effect of fertilizer N (prilled urea-PU) and briquettes-urea supergranules (USG) on rice yield performance and nutrient uptake was investigated in West Africa. Field experiments were carried out in Sourou valley in Burkina Faso in the wet season of 2012 and dry season of 2013. PU was broadcast applied and USG were point-placed deeply into the soil at 5-7 cm using the same fertilizer N rates (52 kg N ha) and two different rice varieties (FKR 19 and NERICA 62N). The results indicate that Fertilizer Deep Placement (FDP) significantly increased grain yields, particularly in the wet season as compared with broadcasting. The FDP applied to NERICA 62N produced the highest tillers and panicles numbers, leading to more yields. In wet season, FDP significantly increased agronomic efficiency by 39.43 % over PU and physiological efficiency by 24.23 %. In the dry season, differences in the average nitrogen use efficiency (NUE) between FDP and PU were not significant. The studies suggest that FDP is genotype and season-specific, and that it can be used by farmers to improve NUE and increase grain yields in the irrigated rice cropping system. Further investigations are underway to understand seasonal and genetic effect on FDP performance. [ABSTRACT FROM AUTHOR]

Abstract  We have investigated the effect of two nitrification inhibitors, 3,4-dimethylpyrazole phosphate (DMPP) and dicyandiamide (DCD), on the accumulation of $${\text{NH}}^{{\text{ + }}}_{{\text{4}}} {\text{ - N}}$$ and $${\text{NO}}^{ - }_{3} - {\text{N}}$$ after incorporation of cauliflower residues in incubation experiments. Cauliflower leaves were incubated with soil and DCD or DMPP at two application rates [8.93 and 17.9 mg active component (ac) kg−1 for DCD; 0.89 and 1.79 mg ac kg−1 for DMPP]. Both doses of DCD and DMPP increased $${\text{NH}}^{ + }_{4} - {\text{N}}$$ on average by 18.9 and 26.0 mg N kg−1 for DCD1 (during 30 days) and DCD2 (during 45 days), respectively, and on average by 14.4 mg N kg−1 for DMPP1 and DMPP2 during a period of at least 95 days. In DCD-treated soils, $${\text{NO}}^{{\text{ - }}}_{{\text{3}}} {\text{ - N}}$$ data followed an S-shaped curve, indicating that nitrification restarted during the experiment: inhibition was on average 24% during 35 days for DCD1 and on average 45% during 49 days for DCD2. Thereafter, $${\text{NO}}^{ - }_{3} - {\text{N}}$$ amount in DCD-treated soils exceeded that of the cauliflower-only treatment by 31% for DCD1 and 78% for DCD2, probably due to a nitrogen release from DCD itself and a priming effect induced by DCD. In DMPP-treated soils, $${\text{NO}}^{ - }_{3} - {\text{N}}$$ data followed a linear pattern since nitrification was inhibited during the complete incubation (95 days): inhibition was on average 56 and 64% for DMPP1 and DMPP2, respectively. DMPP did not affect the N mineralization of the crop residues. Under favourable conditions, DCD is able to inhibit the nitrification from crop residues for 50 days and DMPP for at least 95 days. Hence, especially DMPP shows a potential to reduce $${\text{NO}}^{ - }_{3} $$ leaching after incorporation of crop residues. [ABSTRACT FROM AUTHOR]